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Chapter 12. Properties of Solutions

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Chapter 12. Properties of Solutions Chapter 12. Properties of Solutions What we will learn: • Types of solutions • Solution process • Interactions in solution • Types of concentration • Concentration units • Solubility and temperature • Solubility and pressure • Colloids GCh12-1 Solution • A homogeneous mixture of two or more substances Saturated solution Unsaturated solution • Contains the maximum amount • Contains less amount of a solute of a solute that will dissolve in a that will dissolve in a solvent solvent Supersaturated solution Crystalization • Contains more amount of a solute • The process in which a dissolved that will dissolve in a solvent (an solute comes out of solution and unstabile state) forms cristals GCh12-2 Types of solutions Comp. 1 Comp. 2 State Examples Gas Gas Gas Air Gas Liquid Liquid Soda water Gas Solid Solid H2 in palladium Liquid Liquid Liquid Ethanol in water Solid Liquid Liquid NaCl in water Solid Solid Solid Brass (Cu/Zn) GCh12-3 Molecular view of solution process During the solution process, solvent molecules interact with solute molecules. If the solvent-solute interactions are stronger than the solvent-solvent and solute-solute interactions, then the solute is dissolved in the solvent. (Energy driven process) Another driving force of the solution process is an increase of dissorder on the final system. If the dissorder of the solution is bigger then dissorder of the solvent and dissorder of the solute, then the solute is dissolved in the solvent. (Entropy driven process) Three steps of solution process (energy driven) D • Heat of separation of solute molecules H1 D • Heat of separation of solvent molecules H2 D • Heat of mixing of solute and solvent molecules H3 GCh12-4 Heat of solution D D D D Hsol = H1 + H2 + H3 Example The endothermic process - solution Exothermic of sodium chloride in water (a favorable process) D Hsol < 0 Endothermic (a non favorable process) D Hsol > 0 GCh12-5 Solubility • Measure of how much a solute will dissolve in a solvent at a particular temperature Like dissolves like • A solute is better dissolved in a solvent, which has similar intermolecular force types and magnites to a solute Ionic molecules are better dissolved Examples in polar solvents • H2O is a good solvent for NaCl Nonpolar molecules are better dissolved in nonpolar solvents • CCl4 is a good solvent for C6H6 GCh12-6 Hydrogen bondings between water and methanol are responsible for solubility of methanol in water Water molecules are stabilizing Na+ and Cl- ions in NaCl solution Dispersion interactions between benzene and CCl4 are responsible for solubility of CCl4 in benzene GCh12-7 Miscible liquids • Two liquids which are completely soluble in each other in all proportions Example • Methanol and water • Ethanol and water • 1,2-ethylene glycol and water GCh12-8 Solvation • The process in which a solute molecule (ion) is surrounded by solvent molecules There are several solvation spheres. The solvation process involving water molecules is called hydration GCh12-9 Problem Predict the relative solubility in the following cases: a) Bromine (Br2) in benzene (C6H6) and in water b) KCl in carbon tetrachoride (CCl4) and in liquid ammonia (NH3) c) Formaldehyde (CH2O) in carbon disulfide (CS2) and in water m = 1.87 D m = 2.33 D m = 1.46 D GCh12-10 Concentration units • Percent by mass (units: %), is independent of temperature and does not require calculations of molar masses • Mole fraction (no units); is used in calculating partial pressures of gases • Molarity (units: mol/L); used practically in laboratories because a volume of a solution is easy to measure, but is dependent of temperature • Molality (units: mol/kg); is independent of temperature because the concentration is expressed in solute number of moles and mass of solvent GCh12-11 Percent by mass mass of solute (msl) = X 100% (units %) mass of solute (msl) + mass of solvent (msv) Example What is the percent by mass of 0.892 g KCl dissolved in 54.6 g water. Data msl - mass of solute = 0.892 g msv - mass of solvent = 54.6 g Solution percent by mass = 0.892 g / (0.892 g + 54.6 g) X 100 % = 1.61 % GCh12-12 Mole fraction moles of solute (nsl) X = (no units) moles of solute (nsl) + moles of solvent (nsv) Example What is the mole fraction of 12.5 g sodium chloride (NaCl) dissolved in 80.5 g water. Data Number of water moles: m - mass of solute = 12.5 g sl 1 mol = 18.02 g msv - mass of solvent = 80.5 g n mol = 80.5 g Solution n = 1 mol x 80.5 g / 18.02 g Step 1. Calculation of moles: = 4.46 mol nsv = 4.46 mol GCh12-13 GCh12-14 Step 2. Calculation of moles Number of NaCl moles: nsl = 0.21 mol 1 mol = 58.44 g n mol = 12.5 g n = 1 mol x 12.5 g / 58.44 g = 0.21 mol Step 3. Calculation of mole fraction mole fraction = 0.21 mol / (0.21 mol + 4.46 mol) = 0.04 GCh12-15 Molarity moles of solute (nsl) M = (units: mol / L) volume of solution (Vsn) Example Calculate molarity of a 1.2 L of HNO3 solution containing 24.4 g of HNO3. Data msl - mass of solute = 24.4 g Vsn - volume of solution = 1.2 L GCh12-16 Solution Number of HNO3 moles Step 1. Calculation of moles 1 mol = 63.02 g nsl = 0.38 mol n mol = 24.4 g Step 2. Calculation of molarity n = 1 mol x 24.4 g / 63.02 g = 0.38 mol molarity = 0.38 mol / 1.2 L = 0.31 mol/L GCh12-17 Molality moles of solute (nsl) m = (units: mol / kg) mass of solvent (msv) Example Calculate the molality of H2SO4 solution, containing 24.4 g of H2SO4 in 198 g of water. Data msl - mass of solute = 24.4 g msv - mass of solvent = 198 g = 0.98 kg GCh12-18 Solution Number of H SO moles Step 1. Calculation of moles: 2 4 1 mol = 98.10 g nsl = 0.24 mol n mol = 24.4 g n = 1 mol x 24.4 g / 98.10 g Step 2. Calculation of molality: = 0.24 mol nsl = 0.24 mol /0.98 kg = 1.26 mol / kg GCh12-19 Density of solution mass of solution (msn) d = (units: g / mL) volume of solution (Vsn) Examples msn - mass of solution = 128 g Vsn - volume of solution = 1.45 L = 1450 mL d = 128 g / 1450 mL = 0.08 g/mL GCh12-20 Problem The molarity if a aqueous solution of methanol is 2.45 M. The density of this solution is 0.976 g/mL. What is the molality of the soltuion. Data dsn - density of solution = 0.976 g/mL Msn - molarity of solution = 2.45 M Solution moles of solute (nsl) mass of solution (msn) M = d = volume of solution (Vsn) volume of solution (Vsn) moles of solute (nsl) m = mass of solvent (msv) GCh12-21 Step 1. Calculation of mass of solute Mass of CH OH: 2.45 moles - 1 liter of solution 3 1 mol = 32.04 g 79.49 g - 1 liter of solution 2.45 mol = n g n = 2.45 mol x 32.04 g / 1mol = 79.49 g Step 2. Calculation of mass of water 0.976g of solution - 1 mliter of solution 976 g of solution - 1 liter of solution mass of water = 976 g - 76.49 g = 898 g GCh12-22 Step 3. Calculation of molality: m = 2.45 mol / 0.898 kg = 2.73 m GCh12-23 Problem The density of an aqueous solution containing 10 % of ethanol (C2H2OH) by mass, is 0.984 g/mL. Calculate the molality of this solution. Calculate the molarity Data dsn - density of solution = 0.984 g/mL P - percent by mass of solution = 10% moles of solute (n ) sl mass of solution (msn) M = d = volume of solution (V ) sn volume of solution (Vsn) moles of solute (nsl) m = mass of solvent (msv) GCh12-24 Step 1. Calculation of mass of water in 100 g Moles of ethanol: of solution 1 mol = 46.07 g 10g (E) - 100g (S) n mol = 10 g m (W) = 100 g (S) - 10 g(E) n = 10 g x 1 mol / 46.07 g = 90 g = 0.09 kg = 0.217 mol Step 2. Calculation of ethanol moles in 100 g of solution 10g (E) (1 mol) / (46.07 g) = 0.217 mol (E) Step 3. Calculation of molality of 100 g of solution m = (0.217 mol) / (0.09 kg) = 2.41 mol/kg GCh12-25 Step 4. Calculation of a volume of 100 g of Volume of solution: solution 1 mL = 0.984 g 100 g (1 mL ) / (0.984 g) = 102 mL = 0.102 L V mL = 100 g V = 100 g x 1 mL / 0.984 g = 102 mL Step 5. Calculation molarity of 100 g of solution M = (0.217 mol) / (0.102 L) = 2.13 mol/L GCh12-26 Effect of temperature on solubility Solubility • Solubility of solid solutes • Maximal concentration of a • Solubility of gas solutes solute in a solvent Solid solubility Generally, the solubility of solids is bigger at the higher temperature There is no correlation between the solubility of a solute at a particular temperature, and its heat of solution D Hsol • CaCl2 exothermic • NH4NO3 endothermic Solubility of both compounds increases with the temperature GCh12-27 Fractional crystalization • Separation of a solution into pure solutes using their different solubilities By lowering temperature we can extract from a solution a pure solute. If we have a solution of a mixture of two solutes, by using fractional crystalization we can separate those two solutes.
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